Geared limit switch



Jan. 5, 1943. G. E. KING 2,301,514

GEARED LIMIT SWITCH Filed April 11, 1941 Dzfccfzbn f eed WITNESSES:INVENTOR Geo/"ye E King.

BY I

ATTORNEY Plbnted Jan. 5, 1943 it's...

uaeElectrlc Pa, assignor to a- Mahufacturing Commay. East Pittsburgh,Pa, a co poration of lvanla Penney Application April 11, 1041, SerialNo. 388,145 11 Claims. (ta 112-239) My invention relates to acontrol-system for eifecting a predetermined amount of rotation of afeed motor in either of two directions, and is particularly suitable forreciphocable machine tool systems such as planer control systems and thelike. I

Motor operated incremental feed is used quite extensively on planers,plate planers, travelling head planers, planer millers, drawcut andpushcut shapers, etc. The measuring means used to obtain the feed may bea dashpot relay, a geared limit switch or any similar device. Thissystem of control has alrearw been covered by my earlier filed PatentNo. 2,100,745, issued November -30, 1937.

Briefly, this method of control employs the use of a limit switch geareddirectly to the feed motor through a magnetic clutch. The limit switchis reset by a spring when the clutch is deenergized. A dial is providedcalibrated in fractions of an inch for setting the amount of feed, thegearing is usually designed, for example, so that one-quarter revolutionof the motor is equal to one sixty-fourth of an inch feed or 16 motorrevolutions equal one inch of feed.

One outstanding objection to the above scheme such as shown in my priorpatent, is that there is no means of protection against failure of themagnetic clutch. Should the magnetic clutch for any reason such as thefailure of the coil or some piece of apparatus in series with the coilfail to engage, the feed motor would run continuously. This would causethe tool to feed an geared limit switch) is intact to interrupt theenergizing circuit of the motor after a predetermined feeding motion ofthe motor.

A more specific object of my invention is to provide a geared limitswitch for interrupting a feed motor after a predetermined number ofrevolutions, a movable contact member on the armature or operatingmember of an electromagnetic clutch for interrupting the feed motorenergizing'circuit in the event that the clutch which couples the feedmotor to the geared limit switch is not engaged.

, Other objects and advantages will become more apparent from a study ofthe following specification when considered in conjunction with theaccompanying drawing, in which:-

The single figure is a schematic showing of the control system embodyingthe principles of my invention.

Referring more particularly to the figure, M denotes a feed motor havingan armature I, which motor is excited by a suitable field winding 2 froma source of constant potential (not shown). Geared to armature l is anelectromagnetic clutch 3 having an operating coil 4 which when energizedeifects engagement of said clutch. The purpose of the clutch is tocouple or uncouple a measuring means or geared limit switch 5 from thefeed motor through suitable reduction gearing indicated by numeral 6,which measuring means per se is old in the art and is described in myearlier filed patent previously mentioned. It may be briefly describedas comprising a spring biased heart-shaped cam I, which is rotatedeither clockwise or counterclockwise, depending upon whether reversingcontactor I or reversing contactor 9 is energized and having a springbiased pivotedarm Hi, the

roller ii on one end which moves along the periphery of cam I and whichis adopted after predetermined movement of the cam to open spring biasedcontact members l2, so as to effect deenergization of clutch coil 4,hence uncoupling thereof and to effect interruption of contact membersI2 so as to efi ect deenergization of the reversing contactor (I or 9),thereby interrupting the feed circuit of the motor. For simplicity,means for predetermining the necessary angular rotation of cam 1 foreffecting opening of contact members I! is represented as a verticallymovable pivot II, which is moved by an adjustable screw ll alongside acalibrated scale 15.

However, since the specific measuring means.

described above forms no part of my invention, more detailed explanationthereof is not deemed necessary since such can be found in thepreviously mentioned patent.

Since my invention is particularly suitable in a-control system foreifecting reciprocating motion between a cutting tool, such as a planer,and a work piece, it is shown as being associated with such device.However, such planer control 'systems are quite common, and have beendescribed in my previous patents, such as my earlier filed patentmentioned above, and it is felt that merely to show the limit switch l8thereof which. is moved counter-clockwise at the end of the returnstroke by the reciprocating work piece (or in some cases thereciprocating cutting tool,

that is, when the work piece is stationary), soas to close contactmembers l1 thereof and'which limit switchis moved clockwise at the endof the cut stroke so as to close contact members ll thereof. A portionof the reciprocatinglmember is denoted generally by numeral l9 andwhich;

alternately eflects counter-clockwise and clockwise movement of thelimit switch l6. Feed motion is sometimes desirable only at the end ofthe cut stroke and sometimes is desirable only at the end of the returnstroke.

End of stroke selector push buttons "and 2| are provided for efiectingfeed at the end of the return and at the end of the cut stroke; re-

spectively. It will be evident that either of these go switches may beclosed to secure feed at the end of either of the strokes. In addition,a pair of direction of feed" selector push button switche 22 and 23 areprovided for effecting either left or right lateral feed movement bysaid feed mo- 25 tor, that is, either rotation in one direction or in anopposite direction of said feed motors.

The operation of the control system is as follows: When the feed is tostart push button 25 is depressed. A circuit will be completed from oneterminal of the direct-current source indicated'by through the stop pushbutton 26, the

start push button 25 and the'relay coil 2? of relay 28 which eiiectsoperation of relay 28 and closing of contact members 29 which complete aholding circuit around the start push button and sets up a circuit toeither of the directional contactor coils. The limit switch I6 is shownin the position corresponding to the end of the return stroke. At theend of the return stroke a. sea

motor energizing circuit will be established which may be traced fromthe terminal through con- I tact members 39, contact members ii, thepush button 2 l, onset the contact members 52, clutch operating coil 4to the terminal. Energiza= tion ofthe clutch operating coil 4 willattract the armature or operating member 36 thereof which effectsengagement of clutch t against the bias of the spring 35 and at the sametime ef= fects closing of contact members 36, the latter so effectingcompletion of a motor energizing circuit through the right push button23 of the direction of feed" switch and the operating coil of the leftfeed contactor 9. This will effect completion of a circuit from theterminal,

through contact members 31, resistor 38 and armature l-to the terminal,also'through a parallel circuit including resistor 39 and coil so whichwill efiect short circuiting of. resistor 38 shortly after energization.It will be apparent that had the right push button of the direction offeed switch been depressed, the "righ contactor 8 would have beenoperated which would have effected completion of the same circuit, ex-

cept that the direction of energizing current 55 would have beenreversed so as to drive motor in an opposite direction, which is wellknown in the art.

The outstanding feature of my invention cen= ters about a pair ofcontact members 36, one 7 of which is movable and rigidly secured toarma= ture 34 and the other of which is stationary, as shown. It will beapparent that contact members 36 close whenever the coil 4 is energizedto effect engagement of clutch 3. If during feed- :5

ing of the platen (or tool) by the motor l, the

clutch operating coil i should burn out effecting motor energizingcircuit which will causethe feed motor to stop. The feed motor obviouslywill not be able to restart so long as clutch operating coil 4 is notoperative. In other words,

the motor feed circuit can be completed only when the clutch is engagedand is not completed while the clutch is disengaged. Therefore, therecan be no feeding motion of the feed motorunless the timing mechanism orgeared limit switch is intact and ready to interrupt the circuit after apredetermined number of revolutions, In this way, there can be nooverfeeding by the feed motor, which overfeeding might be destructive tothe work piece. or injurious to the operator.

1 am, of course, aware that others, particularly after having had thebenefit of the teachings of my invention, may devise other devicesembodyingmyinventions, and I, therefore, do not wish to be limited tothe specific showings made in the drawings, and the descriptivedisclosure hereinbefore made, but wish to be limited only by the scopeof the appended calims an such prior art that may be pertinent.

I claim as my invention:

1. In a control system for effecting relative reciprocating movementbetween a machine tool element and a work piece element, in combination,a feed motor for effecting lateral incremental feed motions of one ofsaid relatively movable elements at the end of its reciprocatingmovement, an energizing sourceof electrical potential for said motor, alimit switch operable in response to relative motion between the toolelement and work piece, means operable by said limit switch forefiectlng lateral'feed motion of said motor, a circuit interruptingmeans including an electromagnetically operated clutch normally engagedwhile being driven by said motor and being responsive to a predeterminednumber of rotations of said motor tointerrupt said motor energizingcircuit and stop the motor, and means responsive to the operation orsaid clutch to effect interruption of said motor energizing circuit inthe event of failure of theclutch to engage during feeding movement ofthe motor.

2. A control system as set forth in claim 1 in which said clutchincludes an operating member which directly efiects interruption of saidmotor energizing circuit in event of failure of the clutch to engagewhen the motor is operating:

3. A control system as set forth in claim 1 in which said clutchincludes an electromagnet having an armature which acts as an operatingmember for said clutch, a pair of contacts, one of which is carried bysaid armature for effecting interruption of said motor energizingcircuit in the event said clutch fails to engage during rotation of saidmotor.

4. In a control system for eii'ecting relative reciprocating movementbetween a machine tool element and a work piece element, in combination,a feed motor for effecting lateral incremental feed motions of one oisaid relatively movable elements at the end of its reciprocatingmovement, an energizing source of electrical potential for said motor, alimit switch operable in response to relative motion between the toolelement and work piece, and a reversing contactor operable by said limitswitch forselectively efiecting feed motion or said motor in onedirection or an opposite direction, circuit interrupting 'meansincluding an electromagnetically operated clutch normally engaged whilebeing driven by said motor and being responsive to a predeterminednumber of rotations of said motor to interrupt said motor energizingcircuit and stop the motor, and means responsive to the operation ofsaid clutch to eiIect interruption of said motor energizing circuit inthe event of failure of the clutch to engage during feeding movement ofthe motor.

5. A control system as set iorth in claim 4 in which said clutchincludes an operating member which directly operates said circuitinterrupting means in the event of failure of the clutch to engage whenthe motor is operating.

6, A control system as set forth in claim 5 in which said clutchincludes an electromagnet having an armature which acts as an operatingmember for said clutch, a pair of contacts, one of which is carried bysaid armature for effecting interruption of saidmotor energizing circuitin the event said clutch fails to engage during rotation of said motor.

7. In a control system for eii'ecting relative reciprocating movementbetween a machine tool element and a work piece element, in combination,a feed motor for effecting lateral incremental feed motions of one ofsaid relatively movable elements at the end of its reciprocatingmovement, an energizing source of electrical potential for said motor, alimit switch operable in response to relative motion between the toolelement and work piece, a pair of switches each of which is effective tointerrupt said energizing source of electrical potential, transmissionmeans driven by said motor and including a clutch and a revolutioncounting mechanism for operating one of said switches in response to apredetermined number of revolutions of said motor, and means actuated bythe disengaging movement of said clutch for operating the other of saidswitches to effect interruption of said energizing source.

8. A control system as set forth in claim '7 in which said clutchincludes an electromagnetic operator having an armature and in whichsaid last mentioned means includes a contact member rigidly secured tosaid armature and a cooperating stationary contact member.

9. A control system for effecting a lateral feeding movement of areciprocable machine tool element at recurrent intervals comprising, incombination, a feed motor for effecting said lateral feed movement,driven by said motor including aclutch and a revolution counter, acircuit interrupter which is operable in response to a predeterminednumber of revolutions of said motor as measured by said revolutioncounter for efiecting deenergization and stoppage of said motor, asecond circuit interrupter which is directly operated by one of theelements of said clutch for effecting deenergization of said motorwhenever said clutch is disengaged.

10. A control system as set forth in claim 9 in which said clutch iselectromagnetically operated, including an armature which serves as anoperating member and in which one of the contact members of said secondcircuit interrupter is rigidly secured to said armature.

11. In a system for controlling movement of an element, a drive forimparting movement to the element, means for measuring the movement ofsaid element and for stopping said drive after movement of said elementa predetermined distance, a clutch connecting said measuring means tosaid drive for rendering said measuring means operative, and meansoperative upon failure of said clutch for stopping said drive prior tooperation of saidmeasuring means.

GEORGE E. KING.

transmission means

